<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .common {
            border-top-color: #ffc107;
            border-right-color: #00bcd4;
            border-bottom-color: #e26b6b;
            border-left-color: #cc7cda;
            border-width: 50px;
            border-style: solid;
        }
        /* 直角三角形 */
        .right-aligned{
            border-left: 30px solid rebeccapurple;
            border-bottom: 30px solid transparent;
        }
        /* 等腰三角形 */
        .isoceles {
            border-left: 30px solid red;
            border-top: 15px solid transparent;
            border-bottom: 15px solid transparent;
        }
    </style>
</head>

<body>
    <div class="common"></div>
    <hr>
    <div class="right-aligned"></div>   
    <hr>
    <div class="isoceles"></div>     
</body>

</html>